Peristaltic pump and system therefor

ABSTRACT

A peristaltic pump is provided, which may have auxiliary fluid introduction, for a plurality of resilient pump tubes progressively occluded concurrently along a portion of their lengths, recurringly, to advance fluids therethrough by a pressure roller assembly; and a control system for the pump to render the roller assembly inoperative to advance fluids. A platen is mounted for movement from an operative position, in which the pump tubes are engaged and sandwiched between the platen and the roller assembly, to an inoperative position in a direction away from the roller assembly. In the inoperative position of the platen, a tube or tubes of the auxiliary fluid introduction, which includes a pressure pin cooperating with a pad engageable with the tube or tubes therebetween, are released. The platen is power-operated to move to at least one of the two aforementioned positions thereof.

United States Patent 1 Kling, deceased PEIUSTALTIC PUMP AND SYSTEM THEREFOR [75] inventor: Nelson G. Kling, deceased, late of Ocala, Fla. by Alice Irene Kling, administratrix [73] Assignee: Technicon Instruments Corporation,

Tarrytown, NY.

[22] Filed: Sept. 14, 1970 [21] Appl. No.: 71,773

Weiskopf et al ..4 1 7/475 [451 May 1, 1973 3,588,281 6/1971 Isreeli et a1. ..4l7/53 Primary ExaminerCarlt0n R. Croyle Assistant ExaminerRichard E. Glluck Attorney-S. P. Tedesco and S. E. Rockwell 5 7 ABSTRACT A peristaltic pump is provided, which may have auxiliary fluid introduction, for a plurality of resilient pump tubes progressively occluded concurrently along a portion of their lengths, recurringly, to advance fluids therethrough by a pressure roller assembly; and a control system for the pump to render the roller as sembly inoperative to advance fluids. A platen is mounted for movement from an operative position, in which the pump tubes are engaged and sandwiched between the platen and the roller assembly, to an inoperative position in a direction away from the roller assembly. In the inoperative position of the platen, a tube or tubes of the auxiliary fluid introduction, which includes a pressure pin cooperating with a pad engageable with the tube or tubes therebetween, are released. The platen is power-operated to move to at least one of the two aforementioned positions thereof.

7 Claims, 5 Drawing Figures Patented May '1, 1973 3,730,650

2 Sheets-Sheet 1 IJIVLZPCIUf-L NELSON G KUNG,

Patented May 1, 1973 2 Sheets-Sheet 2 64 20 X r 10 I '20 e4 V I mill -F IG,-4 v

n I l 1 l 111 J a, il 'l I h as 28 PLATEN/ m T0 SAMPLER PUMP Ml mums W rind, nmue SlGNAL m PRESSURE 4'30 SOURCE PERISTAILTIC PUMP AND SYSTEM THEREFOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to fluid pumps, and particularly to peristaltic type proportioning pumps utilizing compressible tubes, which are advantageously utilized in flowing stream analytical systems.

2. Description of the Prior Art In systems of this kind, a flowing stream of sample liquid, which stream may be a continuous monitoring stream, or a stream of sequential liquid samples, may be continuously mixed in a predetermined proportion with one or more reagents, and may be otherwise processed to provide, say, a color reaction, the optical density of which at a particular wave length is responsive to the concentration of a constituent of interest in the sample. Such a system is illustrated and described in US. Pat. No. 2,797,149 issued June 25, 1957.

A peristaltic pump suitable for use in such a system is illustrated and described in US. Pat. No. 3,425,357 issued Feb. 4, 1969, having auxiliary fluid introduction for the purpose of maintaining constant the proportions of reagents and samples, which proportioning problem was earlier recognized and described in US. Pat. No. 3,306,229 issued Feb. 28, 1967.

In addition to the roller assembly coacting with pump tubes, the pump of U.S. Pat. No. 3,425,357, supra, included in the auxiliary fluid introduction, a pressure pin and pad for periodically occluding therebetween at least one fluid tube, and a mechanism to release the tube periodically for flow therethrough, once between the separation of successive rollers from the roller tubes. According to the last-mentioned patent, a linkage was provided coupling the platen to the aforementioned pad so that release of the platen from the roller tubes effected release of the tube or tubes from the pressure pin and pad.

That patent illustrates and describes, among other features of the pump, a pressure roller assembly, with'a coacting platen assembly, which is inverted with reference to the corresponding assembly of US. Pat. No. 3,306,229, supra, and that illustrated and described in an earlier U. S. Pat. No. 2,935,028 granted May 3, 1960.

The pressure roller assembly of US. Pat. No. 3,425,357, supra, coacts with a platen assembly located above it, which platen assembly is swingable manually on an axis, in a manner similar to the aforementioned earlier pressure roller assemblies, to clear the pump tubes and relieve stress thereon when the pump will not be in use for a period of time, thereby lengthening the service life of the pump tubes. This not only requires the person operating the system to remember to relieve pressure on the pump tubes when the pump is not in use, but also to make the effort to disengage manually the platen from the tubes. This procedure could be forgotten, with resultant tube failure, and was a nuisance. The present invention obviates the necessity of manipulation of either the pressure roller assembly or the platen assembly to relieve stress on the pump tubes.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved peristaltic pump of the type having auxiliary fluid introduction as aforesaid including a mechanism for occluding a fluid tube and timing the release of fluid therefrom, for constant uniform proportioning of the fluids advanced by the pump, wherein provision is made for the release from compression of all the tubes including the release of compression of the fluid-supply tube of the aforementioned auxiliary mechanism, when the pump is not in use, thereby precluding the development of a permanent set in any of these tubes.

Another object is to provide in such a pump, a platen mounted to occupy an operative position and an inoperative position, and power operated means to move the platen to one of these positions. There is also provided in such a pump a platen which is self-moving to the other position. 1

Still another object is to provide such a pump in a system wherein the system has a fail-safe feature operative to release the pump platen from the pump tubes.

BRIEF DESCRIPTION OF THE DRAWINGS In thedrawing FIG. l is a top plane view of a peristaltic proportioning pump embodying the invention; 7

FIG. 2 is a sectional view taken on line 2-2 of FIG.

FIG. 3 is a sectional view taken on line 3-3 of FIG.

FIG. 4 is an elevational view looking in the direction of the arrows 44 of FIG. 1;

FIG. 5 is a diagramatic view of a system in which the pump of the invention may be a part.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As indicated particularly in FIG. I of the drawings, the pump of the invention is of the type illustrated and described in US. Pat. No. 3,425,357, supra, the disclosure of which is hereby incorporated by reference. The pump of the last-mentioned patent is an improvement of the pump of US. Pat. No. 3,306,229, supra, the disclosure of which is also hereby incorporated by reference.

Briefly, the pump includes an outer box-like housing 10 (FIG. 1) wherein a pressure device (FIG. 2), indicated generally at 12, is supported which includes two spaced-apart sprocket chains, one being indicated at 14, such as described in US. Pat. No. 3,425,357, which are associated with spaced-apart respective guide plates, one being indicated at 18. The sprocket chains are driven in the manner illustrated and described in the last-mentioned patent. A plurality of rollers 16 are journaled by and between the two sprocket chains and these rollers engage and pass over the aforementioned guide plates.

A cover assembly, indicated generally at 20 has two side walls 22 each of which has on an extension thereof a hook portion 24 adapted to fit under and pivot about a respective horizontal stud 26 fixed to the housing. The cover assembly 20 includes a platen assembly, indicated generally at 28, and best shown in FIGS. 2, 3 and 4. The platen assembly 28, supported by the cover assembly 20, extends into an aperture 30 formed in the top of the housing 10. A pair of grooved, spaced apart, pump-tube-locating blocks 32 are releasably mounted in a conventional manner on the top of the housing adjacent the aperture 30 therein at opposite sides thereof.

A plurality of pump tubes 34, 34a, may be disposed between the two blocks 32 over the aperture 30 in side by side relation as shown in FIG. 1. Collars 36 fixed to the respective pump tubes in pairs abut the respective blocks 32 to support the tubes as shown in the lastmentioned view.

When the cover assembly carrying the platen assembly 28 is swung down to the position shown in FIG. 2 and latched in place by latch assemblies, indicated generally at 38, in the manner disclosed in the lastmentioned patent, the pump tubes may be pressed downwardly subsequently, in a manner to be described hereinafter, by the lower face of the lower part of the platen assembly 28 against those rollers 16 which are riding on the upper edges of the guide plates 18, so that the tubes are occluded by these rollers as indicated in FIG. 2. When these rollers are advanced by the sprocket chains they progressively occlude these tubes along their respective adjacent lengths, advancing such fluids as are contained therein. It will be noted that at least two rollers are always in occluding engagement with the tubes. The pump tubes 34 and 34a are customarily made of a compressible resilient material such as polyvinyl chloride sold under the trademark Tigon.

It will be appreciated that while a peristaltic type pump utilizing a plurality of rollers has been illustrated, any tube occluding means which is regularly periodically operated, such as a cam, or a series of fingers, may be utilized in the pressure assembly.

The cover assembly 20, together with the platen assembly 28, is completely removable from the pump housing for complete access to the pump tubes. To mount the cover assembly with the platen to the housing 10, the aforementioned hooks 24 of the side walls are engaged under the studs 26 and the cover and platen assemblies are swung as a unit downwardly, on an axis to the position shown in FIG. 2, to be latched as aforesaid by the aforementioned latch assemblies 38 shown in FIG. 1. It will be understood from the foregoing that the cover assembly with the platen assembly 28, after being unlatched, may be swung upwardly on the last-mentioned pivotal axis from the positions of FIGS. 1 and 2 without the removal thereof from the pump.

Referring again to FIG. 1, one of the pump tubes 34 may convey sample while the other illustrated pump tube 34 may convey a reagent. Pat. No. 3,306,229, supra, describes to some extent, as does Pat. No. 3,425,357, supra, the desirability of controlling the input of a segmenting fluid, which may be gas, into the sample tube or the reagent tube downstream from the pump in a conventional junction, not shown. In the present illustration, this segmenting fluid may be conveyed by the pump tube 34a which is shown in a position to be acted upon by the pump to convey fluid therethrough. However, as indicated in US. Pat. No. 3,306,229, supra, this fluid admitting tubeneed not have the fluid conveyed therein by the pump but may be supplied from an external source, such as a container of pressurized gas for example.

Specifically the pump tube 34a for advancing the segmenting fluid is pinched closed, except when the fluid therein is to be released. It is also desirable that this pinching be released when the pumping operation is discontinued to avoid a permanent set in the tube, as indicated in U.S. Pat. No. 3,425,357, supra.

A fluid tube block assembly, indicated generally at 39, is disposed on the top of the housing 10. This assembly includes a U-shaped block support 40 having two spaced-apart upstanding legs 42 and conventionally fixed to the top of the housing. A shaft 44 is journaled between and through these legs 42. A fluid tube support plate 46 is pivotly journaled on the shaft 44. This plate includes cars 48 by which the plate is journaled on the shaft 44, and further includes a plate portion 50 having two spaced-apart pluralities of upstanding spaced-apart teeth, as shown in FIG. 1, which provide tube receiving grooves therebetween. A tube 340 can be seen to be located in appropriate ones of these grooves. A resilient pad 52 is adhered to the top of the plate between the two series of teeth. Rearwardly, the plate 46 has an inverted L-shaped portion A pressure pin 56 is fixed to the shaft 44 by two spaced-apart arms 53. The distal ends of these arms 58 are fixed to the shaft 44. The pressure pin 56 is operated by the shaft 44, which has a rocking movement, through an operative connection to the rollers 16 of the pressure device in a manner which forms no part of the present invention and is fully described in Us. Pat. No. 3,425,357, supra. The pressure pin 56 presses the pump tube 34a against the pad 52 to occlude the tube except at intervals dictated by the movement of the tube rollers when the pump is in operation. The pressure pin element 56 coacting with the pad element 52 to occlude periodically the tube 34a conveying the segmenting fluid forms the aforementioned auxiliary fluid introduction part of the pump mechanism.

With reference to the cover assembly 20, supporting the platen assembly 28 constructed for power operation, the construction and arrangement of which parts of these assemblies are closely related, it may be noted first that the platen assembly 28, in the illustrated form of the invention, is moved to the operative position thereof by power, after the cover assembly is latched in position as aforesaid by the latch mechanisms 38. This subassembly of the pump includes a relatively thick metal plate 60 secured to the aforementioned side walls 22 as by suitable fasteners, not shown, which walls depend from the plate 60, one of which is shown in FIG. 3 in this relationship. The plate 60 has a central opening defined by a cylinder wall 62 as shown in FIG. 2. The plate 60 is horizontally arranged and the cylinder wall is upwardly arranged, having an open lower end as shown in the last mentioned view.

Closing the upper end of the cylinder is a cover plate 64 which sandwiches a diaphragm 66, which may be structured of rubberized fabric, between itself and the upper end of the cylinder 62 by being interposed between a flange of the cover plate 64 and the upper surface of the plate 60. The cover plate 64, the diaphragm 66 and the plate 60 are secured together in the area of the last-mentioned flange by suitable fasteners not shown.

As shown in FIG. 2 the cover plate 64 has the shape of an inverted dish and is round in outline as seen in FIG. 1.

A relatively thick metal plate of circular outline forms a piston 68 received in the cylinder 62 with clearance as shown in FIG. 2. The diaphragm 66 has a central opening the marginal portion of which extends over the piston 68 and is secured thereto by an overlying plate 70. A relative thick metal plate 72 abuts the bottom of the piston 68 in flatwise relation and forms at least a part of the platen assembly 28. The lower face of the plate 72, indicated in FIG. 2 to be in engagement with the pump roller tubes, has rounded marginal portions as shown, and if desired, this face of the plate 72 may be covered with a sheet of suitable cushioning material not shown. Fasteners 74 extend through the plate 70, the diaphragm 66, the piston 68 and into the platen 72 to secure these elements together, one being shown in FIG. 2. The platen 72 may be oblong with its longest dimension arranged transversely as the pump tubes 34, 34a.

As shown in FIG. 2 the piston 68 has a central opening 76 extending axially therethrough and in alignment with the cavity 78 directed upwardly in the platen 72. A sealing ring 79 may be interposed between the piston 68 and the platen 72 in an enlargement of the bore 76.

A vertical stub shaft 80 has a reduced end portion thereof extending upwardly through the center of the cover plate 64 and secured to the top of the plate 64 as by having a nut 82 threaded thereon. The portion of the shaft of larger diameter abuts the underside of the plate 64 in the manner shown in FIG. 2, so that the shaft depends from and is fixed to the cover plate 64. The lastmentioned shaft 80 has at the lower end thereof a radial flange 84. The shaft 80 extends through a bushing 86 which has a radial flange 88 abuting the underside of the plate 70. A helical spring 90 surrounding the bushing is compressed between the aforementioned flange 88 of the bushing and the aforementioned radial flange 84 of the shaft, which. spring has the action of urging the piston 68 and the platen 72 in an upward direction to the position shown in phantom in FIG. 2 in which the platen 72 is in the inoperative position thereof. In the last-mentioned position the upper surface of the plate 72 providing the platen abuts the underside of plate 60 which acts as a stop to limit upward travel of the platen To prevent angular movement of the piston 68 with its associated parts in the cylinder provided by the plate 60, guide pins are vertically arranged and fixed to the cover 64 in a manner to depend therefrom to coact with guide openings in the plate 68,-one such guide pin 92 being shown in FIG. 2 cooperating with one such guide opening 94. Also as shown in the last-mentioned view, the cover plate 64 has a fluid inlet tube 96 extending therethrough for admission of fluid above the piston 68 and the diaphragm 66. It will be understood from the foregoing that fluid admitted to the tube 96 serves to force the piston 68, through movement of the diaphragm 66, in a downward direction carrying with it the platen 72, for engagement of the platen assembly with the roller pump tubes in the manner shown in FIG. 2. Fluid may be vented through the tube 96, on which occasion the spring 90 serves to return the piston 68 and the platen 72 to the upper positions thereof in which the pump tubes are cleared by the platen asthese tubes. The travel of the platen assembly 28 to the inoperative position may be approximated 0.50 inch. A simple conventional limit switch, not shown, may be operated on upward movement up the platen assembly 28 to its inoperative position thereof to discontinue the driving connection to the sprocket chains 14 carrying the tube rollers 16, and thereby shut down the pump.

The operative connection between the piston 68 or the platen 72 to the fluid tube block assembly 39, which serves to release pinching pressure on the fluid tube 34a, when the platen assembly 28 is in the inoperative position thereof, will now be described. This operative connection includes a lever 98, best shown in FIG. 4, one end of which is forked, as at 100, to receive the end of a pin 102 extending horizontally and fixed in the platen plate 72 in a conventional manner. The forked end 100 of the lever receiving the pin 102 is shown to advantage in FIG. 3.

Intermediate of its ends the lever 98 is pivoted, as at 104, to one of the walls 22 fixed to the cylinder 60. The other end of the lever 98 (FIGS. 1 and 4) has a laterally directed finger 106 underlying the inverted L-shaped portion 54 of the plate 46 pivoted to swing on the shaft 44 as previously described. When the lever 98 is in the full line position of FIG. 4 the plate 46 is maintained in a position to coact with the pressure pin 56 so that the latter may periodically occlude the pump tube 34a in the manner previously discussed. However, when the platen assembly 28 is raised to the inoperative position thereof the lever 98 is swung on the axis of its pivot 104 from the full line position of FIG. 4 to the position shown in phantom in which the plate portion 54 may swing downwardly, following the lowering, swinging movement of the finger 106 of the lever, thereby releasing the tube 34a from the pressure pad 56 carried by the plate 46, so that the tube 34a may re-expand.

The previously described pump may be used in a system such as shown in FIG. 5 which may be a part of an automated analytical system such as that illustrated and described in US. Pat. No. 3,241,432 issued Mar. 22, 1966. There is indicated at 108 a pressure source which may be either a pump or a pressurized container of fluid such as a gas. For the purpose of example the pressure source 108 may be considered as a pressurized container of gas having an outlet in which is interposed a pressure regulator 110. Branching off this outlet is a tube 112 to pressurize a container 114 which may be filled with a fluid such as a liquid reagent. Connected to the aforementioned outlet of the pressuresource 108, as shown in FIG. 5, is a tube 116 connected to a valve 1 18, controlled by a timing signal 120, which valve may be of the three-way type to interconnect through the valve 118 the tube 116 and a tube 122 or connect the tubes 116, 122 to the ambient atmosphere through a a I vent. The tube 122 is connected to the inlet tube 96 previously described in the pump. It will be evident from the foregoing that fluid entering the tube'96 against the pressure of the pump spring operates to move the platen assembly 28 of the pump to the operative position thereof in which fluid may be conveyed by the pump. a

A sampler, indicated at 124, may be of the type illustrated as described in U.S. Pat. No. 2,879,141, issued Mar. 24, 1959, in which successive sample cups are presented to a station whereat an aspirating tube aspirates that particular sample to direct it through a tube such as the tube 126 showin in FIG. of the present drawings. Suction is provided in the tube 126 by the operation of the pump in the aforementioned manner which pump, solely for purposes of example, is shown as operatively connected only to the tube 126. Other fluid lines may, of course, be added as desired.

A tube 128 extends from the pressurized container 114 of reagent or-the-like for the exit therefrom under pressure of the reagent which is directed by the tube 128 to a flow control device 130 from which it exits at a lower rate in a tube 132. The tube 132 is branched to the pump outlet shown in FIG. 5 in which the reagent joins the sample upstream of a mixer 134, which may be of the coil type, in which the ingredients of the stream are well mixed together. As indicated in the lastmentioned view the stream then passes downstream from the mixer directly to analysis apparatus or for further treatment prior to analysis, which analysis may take the form of examination in a colorimeter or in a flame photometer. The sample stream flowing into and from the pump may be segmented by a fluid such as a gas, if desired, as by being provided with gas segments through the operation of the pump, through the inlet of gas through the tube 126 between samples or by other means. This segmenting fluid tends to maintain sample integrity, as by separating samples one from another, and also serves to cleanse the tubing walls.

The timing signal 120, controlling the valve 1 18 and through it the position of the pump platen assembly 28, may be controlled in a variety of ways which will be apparent to one versed in the art. Obviously, the timing signal may be controlled by a master switch, not shown, operative to turn off the entire system including the portion of the system shown in FIG. 5. The timing signal 120 may also be controlled by a known device for detecting clogging in a fluid line such as a sample line, as illustrated and described in US. Patent 3,424,557 issued January 28, 1969, for example. It may be operated by a leak detector of the conductivity type, which is also known, associated with the pump. Still further, it might be governed by a malfunction detector such as a pressure sensor or a malfunction detector of the type sensing flow rates as illustrated and described in US. Patent 3,529,635 issued September 22, 1970, for example.

It is believed that many advantages of this invention will now be apparent to those skilled in the art. The foregoing description is illustrative, rather than limiting, as a number of variations and modifications may be made without departing from the true spirit and scope of the invention. The invention is limited only by the scope of the following claims.

WHAT IS CLAIMED IS:

1. A fluid analysis system for transport of a sample comprising a support, a plurality of fluid-conveying pump tubes on the support, a platen assembly to back the pump tubes, a pressure assembly having means operable to engage concurrently and progressively occlude said tubes against said platen along their lengths, and to release said tubes, at least one of said tubes being connected to a source of sample for transport of the latter, one of said assemblies being movably mounted on said support to shift to occupy an operative position in which said tubesare compressed and to occupy an inoperative position in which said tubes are released from pressure thereon by the last-mentioned assembly, and power-operated means to move said one of the assemblies to each of said positions, a pressure source, a conduit connecting the pressure source to said power operated means, a vent valve located in the conduit, said vent valve responsive to a malfunction of said system to vent the power-operated means and thereby shift the movable assembly to said inoperative position rendering the system inoperative.

2. A system as defined in claim 1, wherein: said movable assembly is removably mounted on said support for access to the pump tubes.

I 3. A system as defined in claim 1, wherein: said movable assembly is mounted so as to be swingable on an axis for access to the pump tubes.

4. A system as defined in claim 1, wherein: said movable assembly is the platen.

5. A system as defined in claim 1, wherein said movable assembly is the platen and said means to shift the platen to said positions thereof comprises a piston operated by fluid pressure.

6. In an analysis system for transporting a sample, a peristaltic pump comprising a support; a plurality of pump tubes on the support; a platen assembly to back the pump tubes; a pressure assembly having means operable to engage concurrently and progressively occlude said tubes against said platen along their length, and to release said tubes; one of said assemblies being movably mounted on said support to shift rectilinearly to occupy an operative position in which said tubes are compressed and occupy an inoperative position in which said tubes are released from pressure thereon by the last-mentioned assembly; fluid-operated means to move the last-mentioned assembly to one of said positions; a fluid pressure source; conduit-forming means between said pressure source and said fluid-operated means; the pressure source being connected to a source of reagent to pressurize the last-mentioned source for transport of the reagent for mixture with the sample; and valve means to vent said fluid-operated means.

7. An analysis system as defined in claim 6: further comprising a timing signal device having an operative connection to said valve means to operate the latter to vent said fluid-operated means. 

1. A fluid analysis system for transport of a sample comprising a support, a plurality of fluid-conveying pump tubes on the support, a platen assembly to back the pump tubes, a pressure assembly having means operable to engage concurrently and progressively occlude said tubes against said platen along their lengths, and to release said tubes, at least one of said tubes being connected to a source of sample for transport of the latter, one of said assemblies being movably mounted on said support to shift to occupy an operative position in which said tubes are compressed and to occupy an inoperative position in which said tubes are released from pressure thereon by the lastmentioned assembly, and power-operated means to move said one of the assemblies to each of said positions, a pressure source, a conduit connecting the pressure source to said power operated means, a vent valve located in the conduit, said vent valve responsive to a malfunction of said system to vent the poweroperated means and thereby shift the movable assembly to said inoperative position rendering the system inoperative.
 2. A system as defined in claim 1, wherein: said movable assembly is removably mounted on said support for access to the pump tubes.
 3. A system as defined in claim 1, wherein: said movable assembly is mounted so as to be swingable on an axis for access to the pump tubes.
 4. A system as defined in claim 1, wherein: said movable assembly is the platen.
 5. A system as defined in claim 1, wherein said movable assembly is the platen and said means to shift the platen to said positions thereof comprises a piston operated by fluid pressure.
 6. In an analysis system for transporting a sample, a peristaltic pump comprising a support; a plurality of pump tubes on the support; a platen assembly to back the pump tubes; a pressure assembly having means operable to engage concurrently and progressively occlude said tubes against said platen along their length, and to release said tubes; one of said assemblies being movably mounted on said support to shift rectilinearly to occupy an operative position in which said tubes are compressed and occupy an inoperative position in which said tubes are released from pressure thereon by the last-mentioned assembly; fluid-operated means to move the last-mentioned assembly to one of said positions; a fluid pressure source; conduit-forming means between said pressure source and said fluid-operated means; the pressure source being connected to a source of reagent to pressurize the last-mentioned source for transport of the reagent for mixture with the sample; and valve means to vent said fluid-operated means.
 7. An analysis system as defined in claim 6: further comprising a timing signal device having an operative connection to said valve means to operate the latter to vent said fluid-operated means. 